When I found that python plug-ins do not work, I googled for an explanation.
The file \Apps\GIMP\App\GIMP\lib\gimp\2.0\interpreters\pygimp.interp contains to absolute paths to pythonw.exe

When the drive-letter for the USB-stick changes, it becomes invalid.

Is there a way to use relative paths?
PA seems to rewrite the file when gimpportable starts.

Well, Gimp has a lot of problems

I suggest you to "map a directory" to a virtual drive, i.e., to use "subst" command, like solution I posted to solve a Gimp file recognizing issue: http://www.liberkey.com/forums/topic.ht ... =en#p31853